PC-67: AdminUsers management in ActiveAdmin

[vb-cmd]

Description

• Changed admin_users table to include: ID, Name, Email, Created Date, and Last Sign-in Date
• Added filters for Email and Name
• Changed the show page to include: ID, Name, Email, Created Date
• Added Back button
• Updated the edit and new pages to include: Name, Email, and Password
• Changed the redirect after creating an admin user; now they are redirected to the list.